Method and means for eliminating a selected periodic wave of selected frequency, such as an unmodulated or an amplitude modulated carrier, of which the frequency is herein considered as the frequency of the periodic wave, from a frequency band containing other periodic waves with different frequencies, and non-periodic waves, by sampling and reconstruction means timed from the selected frequency, and by feedback of direct current from the output of the sampling means to the timing circuits.
In the prior art, substantially complete elimination of unwanted waves from a frequency band is disclosed in U.S. Pat. No. 4,249,260, class 455/296, for Noise-Reducing Apparatus, issued Feb. 3, 1981 to Fisher et al., and in U.S. Pat. No. 4,268,914, class 370/118, for Receiving Apparatus for Messages With In-Band Signalling, issued May 19, 1981 to Fisher et al. Neither of these patents discloses negative feedback of dc to the sampling timing circuits, to adjust the sampling instants, which materially improves the elimination of the selected periodic wave, as in this invention.
This invention has utility for use in noise-reduction circuits of the prior art, and in radio and sound location and ranging apparatus, which receives a reflected wave and suppresses a direct wave.